The present invention relates to a yarn piecing method and apparatus for an open-end spinning machine wherein the piecing of the broken yarn end and the restarting of the take-up operation are carried out separately at each spinning unit of the spinning machine without affecting the operation at the other spinning units.
In the open-end spinning machine, the yarn package, the rotor and the feed roll of a spinning unit can be stopped and started again individually in case of the interruption of the spinning operation of the spinning unit. However, the combing roll of the spinning unit is adapted usually to rotate continuously at its working speed of rotation.
If the yarn should break or the yarn package is completely formed, the rotation of the feed roll is stopped, but the combing roll continues to rotate until the broken yarn end is pieced to the fiber by the operator or by the operation of the travelling joining unit. Thus the end of the sliver resting on the feed roll will be opened or broken continuously by the rotating combing roll, and the fiber thus opened is supplied into the rotor with rotation of the combing roll. This fiber has a density and length different to a marked degree from those of the fiber supplied into the rotor during normal spinning. When the yarn should break simultaneously in a plurality of spinning units, the fiber will be worsened further in its length or density since it will take some time until the yarn end is pieced to the fiber. Thus the subsequent yarn piecing will result in failure or formation of an uneven joint in the spun yarn.
It is, therefore, a primary object of the present invention to provide a yarn piecing method wherein the feed roll is rotated for a short time at the time of yarn piecing for delivery of the end of the sliver into the rotor, and the end of the sliver thus supplied is removed from the inside of the rotor, the feed roll being then driven again into rotation for delivery of new fiber to be pieced with the end of the broken yarn.
It is a second object of the present invention to provide a method for cleaning the rotor that will enable a prompt yarn piecing after completion of the cleaning of the rotor. Injection of compressed air into the rotor is convenient in that the cleaning operation may be carried out with the rotor being closed. The present inventors have found that, when the compressed air is injected into the rotor while the latter is rotating slowly, the waste fiber and other impurities that are collected on the inner wall of the rotor may be carried away efficiently by the compressed air. According to the present invention, the braking device for the rotor is actuated in timed relation with the operation of the injection device, and the feed roll is driven in rotation transiently during low-speed rotation of the rotor caused by the actuation of the braking device. The fiber broken from the end of the sliver may thus be discharged from the rotor by the compressed air stream with the dust and dirt collected on the inner wall surface of the rotor. Thereafter, the supply of compressed air is discontinued, while the rotor is released from brake application and accelerated to its working speed of rotation. The various devices are connected operatively with one another for positively cleaning the inside of the rotor in a short period of time. Moreover, this method gives rise to a further advantage. The operation of yarn piecing may be carried out most effectively at the r.p.m. of the rotor equal to 30,000 whereas the number of revolutions of the rotor during normal spinning amounts to about 60,000 r.p.m. Thus the yarn piecing can be carried out at the optimum r.p.m. in the course of accleration of the rotor, the latter being then accelerated to its working speed of rotation after the fiber is pieced successfully to the broken yarn end. It should be noted however that the delivery device adapted for positively withdrawing the yarn from the rotor is rotated at its working speed of rotation as the combing roll. The take-up package is accelerated in correspondence with the acceleration of the rotor. If the yarn should be gripped by the delivery device while the rotor has not attained its working speed, an operative relation between the speed of the take-up package and that of the rotor will be affected adversely thus giving rise to the yarn defect or breakage, as the case may be.
It is the third object of the present invention to get the yarn travel sidewise of the delivery device during acceleration of the rotor and to transfer the yarn into the delivery device when the rotor has attained its working speed of rotation.
To this effect, a threaded roll is mounted in a cantilever fashion to the machine frame in the vicinity of the friction roller of the take-up means. During acceleration of the rotor, the yarn is engaged with the thread formed on the threaded roll and thus kept from being engaged with the traverse guide. This threaded roll is so arranged that, when the yarn has been shifted to the free end face of the threaded roll, it may be brought substantially in contact with the end face of the nip roll which is kept in pressure engagement with the delivery roll. Thus as soon as the yarn is disengaged from the end face of the threaded roll and gripped by the traverse means, the yarn is gripped by and between the nip roll and the delivery roll.
The present invention is applicable most advantageously to a yarn piecing system wherein a yarn piecing unit is provided so as to travel along the front sides of a number of juxtaposed spinning units for detecting the unit or units where yarn break has occurred and automatically piecing the broken yarn in such unit or units without interrupting the continuity in the spinning operation at the remaining spinning units.